JP3347921B2 - PAL color signal phase correction demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase correction apparatus for correcting a phase distortion of a color signal generated in a transmission system in a PAL system of a color television, and more particularly, to a phase correction apparatus having a phase correction circuit disposed downstream of a demodulation circuit. The present invention relates to a PAL type color signal phase correction demodulation device that can be used.

[0002]

2. Description of the Related Art A PAL (Phase Alternation by Line) system in a color television used in Europe and the like uses RY and BY signals as color difference signals. At the time of transmission, the chrominance subcarrier is amplitude-modulated by the chrominance signal and multiplexed with the luminance signal. At this time, the phase of the color subcarrier of the RY signal is inverted by 180 degrees for each scanning line. By utilizing this feature, even if there is a phase shift of the chrominance carrier, this can be corrected at the time of reception to reduce image quality deterioration.

FIG. 2 shows a conventional analog PAL color signal phase correction apparatus. This phase correction device includes a phase correction unit 30 and a demodulation unit 31. First, the color signal E _C1 is input to the phase correction unit 30 and one horizontal scanning period (hereinafter referred to as 1H).
Delay line (1H Delay Line) 3 that delays the signal only
Pass 2 through. A color signal E _C2 for the next scanning line is input,
The calculation with the color signal E _C1 is performed. That is, the color signals E _C1 and E _C2 are added by the adder 33 and subtracted by the subtractor 34 to remove the phase distortion of the color signal E _C.

Here, the correction of the phase distortion of the color difference signal will be described in detail. Figure 3 shows a vector diagram of a color signal _{E C1, E C2, (A} ) shows a color signal E _C1, (B) shows the chrominance signal E _C2 of the next scan line. The color signals E _C1 and E _C2 are respectively
This is a combination of the color difference signals E _BY and E _RY whose phases are shifted by 90 degrees in the orthogonal RY axis and BY axis directions. The _RY axis color difference signal _ERY of the color signals E _C1 and E _C2 is inverted by 180 degrees. Therefore, the addition of the color signals E _C1 and E _C2 results in 2E _BY and the subtraction results in ± 2E _RY .

When the color signals E _C1 and E _C2 are subjected to a phase distortion of Δθ in the transmission system, for example, as shown in FIG.
_C11 and E _C21 change. As described above, in the color signal, the phase distortion of Δθ is reversed every 1H. Therefore, the color difference signals → ± color difference signals → E _BY ± ΔE _BY RY axis BY axis (E _RY ± ΔE _RY). Therefore, as described above, 1H delay line 32
The color signal delayed by H and the color signal of the next scanning line are added to the adder 33.
ΔE _BY ΔE _RY is canceled out by adding / subtracting with the subtractor 34 to correct the phase distortion.

Next, the demodulation unit 31 will be described. Based on the burst signal B, the reference subcarrier E is
Generates _{S (RY)} . This signal is phase-shifted by 90 degrees by a 90-degree phase shift circuit 36 to create a reference subcarrier E _{S (BY)} .
Further, the reference subcarrier-E _{S (RY)} is created by 180 ° by the 180 ° phase shift circuit 37. The color difference signal E _BY is positive only, and only needs to be multiplied by 90 degrees.
_{Since RY} has both positive and negative, it is necessary to demodulate by switching between 0 degree and 180 degrees in order to make this only positive. Therefore, the line discrimination signal f _H is frequency-divided by the flip-flop 38 to generate f _H / 2, and switching is performed using the selector 39. These three reference subcarrier signals, + 2E _BY , ±
Multiply with 2E _RY and demodulate. Thus, PAL
The three types of reference subcarriers necessary for the color signal demodulation of the system are generated.

In the BY demodulation circuit 40, the signal + 2E _BY from the adder 33 and the signal ES _(BY) from the 90-degree phase shift circuit are used.
To generate the color difference signal E _BY . RY demodulation circuit 41
Then, the signal from the subtractor 34 + 2E _RY and the selector 39
By a signal from the E _{S (RY),} or the signal -E S _(RY) from the signal -2E _RY and selector 39 from the subtractor 34, and generates the color difference signals E _RY.

[0008]

If digitization is attempted to improve image quality or the like with the above-described analog circuit configuration, a problem occurs at the 1H delay line.
That is, in the PAL system, the horizontal scanning line cycle T _H = 64 μ
Let s be the frequency of the reference subcarrier f _SC = 4.4336187
When 5 MHz, time T _D for delaying by 1H delay _{line, T D = 1 / f SC} × (283 + 1/2) = 63.943μ
s the <T _H. In order to make a digital signal, it is necessary to perform sampling at f _SC , but it was difficult to sample a half portion, and it was difficult to make a digital signal.

An object of the present invention is to provide a phase correction decoding apparatus of the PAL system chrominance signal capable digital circuit the correction of phase distortion of the PAL system chrominance signal.

[0010]

According to a first aspect of the present invention, a phase distortion of a color difference signal demodulated from a PAL color signal is corrected.
In the phase correction decoding apparatus of the PAL system chrominance signal, Bath
PAL using the reference subcarrier generated based on the
Demodulation unit that demodulates color difference signals from digital color signals of the digital system
And a dot-sequential circuit for dot-sequencing the color difference signal from the demodulation unit.
Path and the dot-sequential signal from the dot-sequencing circuit
Delay by one horizontal scanning period in synchronization with the carrier,
A phase corrector for adding the sequential signal and the delay signal, wherein
Interpolation for separating dot sequential signals from the phase correction unit into color difference signals
It comprising the a circuit.

According to a second aspect of the present invention, the interpolation circuit is configured such that
The next signal is extracted for each half of the reference subcarrier, and
The signal is separated and output as a signal .

[0012]

In the present invention, the phase distortion correction previously performed in the analog system is performed after the color signal demodulation. At the stage of demodulation, the chrominance signal is synchronized with the reference subcarrier signal, and one horizontal scanning period is an integral multiple of the reference subcarrier frequency. Therefore, the 1H delay line is synchronized with the reference subcarrier frequency, thereby enabling a digital circuit. Further, since the signal after the color signal demodulation is only positive, the operation can be performed by the adder, and the number of subtractors can be reduced. In particular, in the second and third inventions, since the color difference signal is unified after the color signal demodulation, the phase distortion can be corrected with one 1H delay line and one adder.

[0014]

FIG. 1 is a block diagram showing an embodiment of a PAL color signal phase correction apparatus according to the present invention. The phase correction apparatus includes a demodulation unit 10 for demodulating a PAL color signal E _C into color difference signals E _BY and E _RY , and a color difference signal E _C.
A dot-sequential circuit 11 for making the dot-sequential signal _BY , _ERY point-sequential, a phase correcting unit 12 for correcting the phase of the dot-sequential signal, and an interpolating circuit 13 for separating the color-difference signals _EBY , _ERY are all digital circuits. is there.

The demodulation unit 10 receives a color signal E _C and a burst signal B which are converted into digital signals by an A / D converter or the like. First, a reference sub-carrier E _{S (RY)} is created by the crystal oscillator 14 based on the burst signal B, and the 90-degree phase shift circuit 1
The phase is shifted 90 degrees at 5 to generate the reference carrier E _{S (BY)} , and 18
The reference carrier-E is shifted by 180 degrees by the 0-degree phase shift circuit 16.
Generate _{S (RY)} . For RY demodulation, a signal for switching between ± _{ES (RY)} is required. Therefore, the line discrimination signal f _H is divided by the flip-flop 17 to generate f _H / 2, which is input to the selector 18 and is supplied with the reference carrier ± E _{S (RY)}
Are switched. E and _{S (BY),} put color signal E _C in BY demodulation circuit 19 to obtain a color difference signal E _BY.
± E _S and _(RY) color signal E _C taking into RY demodulation circuit 11 to obtain the color difference signals E _RY. At this stage, the color difference signal E
_BY and E _RY include phase distortion.

Next, the color difference signals E _BY and E _RY are applied to a dot sequential circuit 1.
A dot sequence is made at 1. With a frequency clock of f _SC / 2,
The function of the dot-sequential circuit 11 is to alternately take in the color difference signals E _BY and E _RY at a fixed period and to integrate the signals into one. This signal is input to the phase correction unit 12.

The phase correction unit 12 includes a 1H delay line 21 and an adder 22. The 1H delay line 21 delays the dot sequential signal by 1H. The dot-sequential signal composed of the color difference signals E _BY and E _RY is synchronized with the frequency of the reference sub-carrier, and the 1H delay line 21 is synchronized with the frequency of the reference sub-carrier. Therefore, unlike the prior art, the signal delayed by 1H is
Sampling at f _SC is possible and there is no problem in digitization. The adder 22 adds the delayed signal and the dot sequential signal. Since the signal is converted into one signal by the dot sequential circuit 11, 1H
Only one delay circuit 21 and one adder 22 are required. Since the demodulated color difference signals E _BY and E _RY both have a positive phase and the phase distortion is inverted every 1H, the phase distortion is removed by adding the same as the conventional color difference signal E _BY. can do. Accordingly, it is not necessary to use a subtracter having a large circuit scale, so that the circuit scale of the phase correction unit 12 can be reduced, so that the entire apparatus can be downsized and the cost can be reduced.

Finally, the dot-sequential signal is input to the interpolation circuit 13 and separated into two color difference signals E _BY and E _RY . The dot-sequential circuit in which the phase distortion has been corrected produces a color difference signal E every f _SC / 2.
_BY and _ERY exist alternately. This signal is expressed as f _SC / 2
And the color difference signals E _BY and E _RY are separated.

The present invention is not limited to such a configuration. A phase correction circuit may be provided for each color difference signal without using a dot sequential circuit.

[0020]

According to the present invention, by correcting the phase by means for delaying one horizontal scanning period after demodulation, the phase distortion can be corrected by a digital circuit. Moreover, since the phase of the color difference signal becomes positive by demodulation, the phase distortion can be eliminated by adding, and the circuit scale can be reduced because it is not necessary to use a subtractor having a large circuit scale. Further, the demodulated signal is set to 1
According to the present invention, the phase correction circuit requires only one delay unit and one addition unit, so that a small and inexpensive device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a PAL color signal phase correction apparatus according to the present invention.

FIG. 2 is a block diagram illustrating an example of a conventional PAL color signal phase correction apparatus.

3A and 3B are vector diagrams of color signals generated by a conventional PAL color signal phase correction apparatus.

[Explanation of symbols]

 Reference Signs List 10 demodulation unit 11 point sequential circuit 12 phase correction unit 13 interpolation circuit 21 1H delay line 22 adder

Claims (2)

(57) [Claims] 1. A color difference signal demodulated from a PAL color signal.
Phase correction recovery of the PAL system color signal for correcting the phase distortion of the issue
In the tuning device, using the reference subcarrier generated based on the burst signal,
Demodulate color difference signal from PAL digital color signal
A demodulation unit, and a dot sequential circuit for converting the color difference signals from the demodulation unit to dot sequence
And the point-sequential signal from the dot-sequencing circuit to the reference subcarrier.
And delays by one horizontal scanning period in synchronization with
And a phase correction unit for adding the delay signal and a point-sequential signal from the phase correction unit into a color difference signal.
Phase correction of the PAL system chrominance signal, characterized by comprising, an interpolation circuit
Demodulator . 2. The interpolation circuit according to claim 1 , wherein the dot sequential signal is
Extracted for each half of the reference subcarrier and separated as a color difference signal
2. The phase correction demodulator for a PAL color signal according to claim 1 , wherein the output is separated.